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Old 10th March 2008, 04:49 AM   #1
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Default LM4780 source questions

I've nearly completed an amplifier for my computer speakers. I purchased the board and a stereo preamp board from veteran. So, this is where I'm at with the whole project: stepped attenuator or a nice potentiometer? I'm not a huge fan of the "clicky-clicky" volume knob, but if there's enough of a difference in sound quality to warrant it, I'll go for it.

Anyone have any input on my conundrum?
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Old 11th March 2008, 09:32 AM   #2
sangram is online now sangram  India
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Channel balancing is much superior on a stepped attenuator, and this is probably a bigger benefit than the absolute SQ vs a carbon pot IMO.

There's an interesting set of posts by Peter Daniel comparing different kinds of volume controls, and he found the TVC to the the best, IIRC.

I've tried both, and in absolute terms I can't really tell a difference - could be the state of my equipment or my ears. However the balance was much superior, leading to a better soundstage. I don't use either anymore, preferring to use the soundcard volume control remotely.
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Old 11th March 2008, 02:51 PM   #3
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I had thought about leaving the front panel blank. My metalworking skills got the best of me. I built a knob that turns around a central post on a bearing. The central post contains the power button and 6 ultrabright LEDs. The knob has a gear mounted to it which drives another gear mounted on another bearing assembly. This will drive my choice of attenuator. I had to build two of these knobs as the first one was out about .012 (I must have dropped it) and it had a noticeable wobble to it.

Anyway, you can see why I would favor something that moves smoothly .

I have a very high end encoder (designed for industrial use). I had contemplated using a microcontroller and some kind of electronic attenuation. It seems like a waste though, considering the use of this amplifier.
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Old 11th March 2008, 05:16 PM   #4
sangram is online now sangram  India
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My main rig is a (almost silent) PC, and I use a remote keyboard and mouse to control it.

Actually all my three setups are PC-based (very basic) and the volume control on the keyboard works dandy for me . I am thankful for not having to go through kxmixer on any of the PCs, by accident or design.

I don't know what resolution you're looking for, but if it's only a casual setup I doubt you'd have much use of a very high-end volume control. Nevertheless it sounds like a boatload of fun to just build it
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Old 12th March 2008, 12:52 PM   #5
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Quote:
Originally posted by sangram
My main rig is a (almost silent) PC, and I use a remote keyboard and mouse to control it.

Actually all my three setups are PC-based (very basic) and the volume control on the keyboard works dandy for me .

I do to, I love having 65535 values to set my volume to. I calculated 30 semi logarithmic steps with a few numbers rounded off.

My amp 5 channel lm3886 amp runs all on "FULL" gain all the time with the main volume to change on my keyboard.
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Old 15th March 2008, 01:35 AM   #6
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Not exactly related, but here are my control boards. Don't click unless your connection is pretty fast. The file is about 5MB.

My first PCB's



They're not exactly Eagle drawings. I downloaded Eagle and even purchased 3X4 boards expressly for the purpose of using it. Unfortunately, I found the interface to be too clunky for my liking. I've used AutoCAD for ages, so I thought I would give it a whirl. I haven't marked components because I know what goes where

These are the first boards I've ever designed. I expect some of the more experienced members to turn up their noses.

The one on the left goes on the bottom, the one on the right on top. There will be ribbon cable connecting to two. The one on the left has a 2.5VA transformer that will stay live. This powers a picaxe microcontroller which will take care of things like soft start, switching a SSR for the main transformers, turning on the LED's, and turning on the speaker output relay. The second board is a Darlington, a 12V regulated supply, and a bunch of terminals.
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Old 15th March 2008, 05:37 AM   #7
sangram is online now sangram  India
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Coverting that file to .gif will drop the size down to 24 KB...
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Old 15th March 2008, 07:07 AM   #8
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I just used the bmpout command in AutoCAD. I know I can convert it, but I was in a hurry.
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Old 15th March 2008, 05:37 PM   #9
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Now in .jpg!

Click the image to open in full size.
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Old 16th March 2008, 05:38 AM   #10
gootee is offline gootee  United States
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Default Re: LM4780 source questions

Quote:
Originally posted by bushroot
I've nearly completed an amplifier for my computer speakers. I purchased the board and a stereo preamp board from veteran. So, this is where I'm at with the whole project: stepped attenuator or a nice potentiometer? I'm not a huge fan of the "clicky-clicky" volume knob, but if there's enough of a difference in sound quality to warrant it, I'll go for it.

Anyone have any input on my conundrum?
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